Hey, I did not have Sobelson, but in my opinion there is no such thing as having a hard professor. You are competing for a rank not necessarily a grade. So if the professor is hard, everyone has the same difficulty. And if the professor is easy then everyone has the same advantage. Your grade is based on one test and you have to figure out how to do better then the 70 other people in your class. If you thought the professor was impossible, maybe everyone else did also.
Just figure out what the professor wants and then get it on paper during your three hour exam. Personally I would rather have a "hard" professor. There is more opportunity to figure out what he wants, and to really analyze the facts and make a good argument on the exam. On "easy" exams everyone spots the issues and there is less opportunity to make an argument that other people did not think of.
Sorry for the long answer to your short question.